Magnetic recording devices generally comprise a thin-film magnetic recording disk and a slider or head which is moved along the surface of the disk to read and/or write information on the disk.
Thin-film magnetic recording disks typically comprise a substrate, such as an aluminum-magnesium alloy with a textured surface coating such as nickel-phosphorous, a magnetic film such as a cobalt based metal alloy or a .gamma.-iron oxide film, and a protective overcoat, such as a sputter-deposited hydrogenated carbon film. A lubricant, such as a polyperfluoroether, is often applied to the carbon overcoat. A general description of the structure of such thin-film disks is given in U.S. Pat. Nos. 4,610,911 to Opfer, et al., and 4,552,820 to Lin, et al.
The lubricant on the surface of the disk functions to reduce wear at the interface of the disk and slider or head as they are moved relative to one another during operation. Excessive wear can eventually lead to failure of the recording device. A second function of the lubricant layer is to reduce the static friction (stiction) between the head and disk. Excessive stiction can also lead to failure of the recording device upon start up.
Prior magnetic recording disks employed liquid lubricants. Liquid lubrication is typically applied via a solvent intensive process using fluorocarbon/chlorofluorocarbon solvents. However, the use of such solvents is being curtailed. Further, liquid lubricants can be depleted due to spin-off during operation. Also, the use of liquid lubricants can result in variations in the thickness of lubricant over disk surface. If the lubricant layer is too thin, it can cause excessive wear and if the layer is too thick, it can cause increased stiction between the head and disk. This is especially true on smooth disks, where capillary forces and meniscus formation lead to unacceptably high stiction at the head/disk interface.
In order to avoid the problems associated with the application of liquid lubricants, gas phase deposition of the lubricant was developed. Yokoyama et al., U.S. Pat. No. 4,816,334, issued Mar. 28, 1989 discloses gas phase deposition of polymeric lubricants onto the surface of magnetic recording disks. The gas phase of the lubricant is created by a variety of techniques such as evaporation, sputtering, ion plating and the like. In evaporation, the gaseous phase of the polymer is formed by heating or by an ion beam impinging on the surface of the polymer. The gas phase is then deposited onto the surface of the disk to form the layer of lubricant. Due to the relatively large size of the gaseous polymer molecules, however, they do not adhere well to the disk surface resulting in a film which is subject to peeling, crazing, cracking or the like. In addition, the gas phase deposition of polymers generally results in a film that exhibits a liquid-like behavior with the associated problem of stiction on smooth disks.
Arai et al., U.S. Pat. No. 4,419,404 issued Dec. 6, 1983, and Imataki et al., U.S. Pat. No. 4,925,733 issued 5/15/90 both disclose forming a polymeric film on the magnetic layer of a recording device by plasma polymerizing organic monomer gases. However, plasma polymerization is deficient because the deposition process, and hence the resultant film composition is difficult to control. This results primarily from the varied species impinging on the disk during the deposition process. For example, a typical plasma comprises ions of both positive and negative polarity (of widely varying energy), electrons, free radicals created from the precursor, and the parent molecule. Therefore, there still is a need in the art for forming an effective lubricating coating on magnetic recording devices.
It is therefore an object of the present invention to provide an improved process for forming a lubricating polymeric coating on a magnetic recording device.
Other objects and advantages will become apparent from the following disclosure.